The Role of Grain Boundaries in the Mechanism of Plasma Immersion Hydrogenation of Nanocrystalline Mg Films

Abstract

In this paper, attention is focused on the nanostructured magnesium films for hydrogen storage. It is shown that 2 μm-thick Mg film is transformed into MgH2 film under high-flux and fluence hydrogen plasma immersion ion implantation at 450 K for 35 min. All hydrogen desorbs at temperature about 530 K, which corresponds to the decomposition of MgH2 → Mg + H2↑. The macroscopic and microscopic observations show that magnesium film undergoes a high deformation during hydrogenation-dehydrogenation reaction. The suggested hydrogenation model is based upon the incorporation of excess of hydrogen atoms in grain boundaries of nanocrystalline Mg film driven by the increase in surface chemical potential associated with the implantation flux. The results provide new aspects of hydriding of thin nanocrystalline film materials under highly non-equilibrium conditions on the surface.